School of Engineering and Technology

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Author: search.filters.author.Tichagwa, LilianEnd date: 2019

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    Preparation of photo‑catalytic copolymer grafted asymmetric membranes (N‑TiO2‑PMAA‑g‑PVDF/PAN) and their application on the degradation of bentazon in water
    (Iran Polymer and Petrochemical Institute, 2016-01-21) Mungondori, Henry Heroe; Tichagwa, Lilian; Katwire, David Meredith; Aoyi, Ochieng
    Nitrogen-doped titanium dioxide (N–TiO2) was prepared and supported on a novel copolymer grafted membrane matrix to avoid the problems associated with the removal of spent photocatalyst from treated water. Membranes of poly (methacrylic acid) grafted onto poly (vinylidene difluoride) and blended with poly (acrylonitrile) (PMAA-g-PVDF/PAN) were prepared through a dry–wet phase inversion technique. Methacrylic acid side chains were grafted onto an activated PVDF backbone by the method of reversible addition fragmentation chain transfer polymerization and then the novel photocatalytic asymmetric membranes of N–TiO2–PMAA-g-PVDF/PAN were prepared. The casting solutions were blended with 1–5 % N–TiO2 before immersion into the coagulation bath. PVDF and PAN offer several advantages which include: mechanical strength and toughness, chemical resistance, unaffected by long-term exposure to UV radiation, low weight, and thermal stability. N–TiO2 was prepared through sol-gel synthesis. The photocatalytic membranes were evaluated by degradation process of herbicide bentazon in water. Photodegradation studies revealed that the optimum photocatalyst loading was 3 % N–TiO2 and the optimum pH was 7 for the degradation of bentazon in water. UV– Vis, TOC and LC–MS analyses confirmed the successful
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    Preparation and Characterization of Polymer-Grafted Montmorillonite-Lignocellulose Nanocomposites by In Situ Intercalative Polymerization
    (Journal of Applied Chemistry, 2016-07-11) Bunhu, Tavengwa; Chaukura, Nhamo; Tichagwa, Lilian
    Lignocellulose-clay nanocomposites were synthesized using an in situ intercalative polymerization method at 60∘ C and a pressure of 1 atm. The ratio of the montmorillonite clay to the lignocellulose ranged from 1 : 9 to 1 : 1 (MMT clay to lignocelluloses, wt%). The adsorbent materials were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and X-ray powder diffraction (XRD). FTIR results showed that the polymers were covalently attached to the nanoclay and the lignocellulose in the nanocomposites. Both TEM and XRD analysis showed that the morphology of the materials ranged from phase-separated to intercalated nanocomposite adsorbents. Improved thermal stability, attributable to the presence of nanoclay, was observed for all the nanocomposites. The nanocomposite materials prepared can potentially be used as adsorbents for the removal of pollutants in water treatment and purification.
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    Competitive sorption of Cd2+ and Pb2+ from a binary aqueous solution by poly (methyl methacrylate)-grafted montmorillonite clay nanocomposite
    (Applied Water Science, 2016-03-24) Tavengwa, Bunhu; Tichagwa, Lilian; Chaukura, Nhamo
    Poly(methyl methacrylate)-grafted montmorillonite (PMMAgMMT) clay and sodium-exchanged montmorillonite (NaMMT) clay were prepared through in situ graft polymerisation and used to remove Cd2+ and Pb2+ from synthetic wastewater. The modification of adsorbent materials was confirmed by fourier transform infra-red spectroscopy (FTIR), thermogravimetric analysis (TGA) and X-ray powder diffraction (XRD) techniques. BET surface area measurements showed NaMMT had a higher surface area than PMMAgMMT. Batch experiments were used to assess the simultaneous uptake of Cd2+ and Pb2+ from a synthetic binary solution. Pb2+ was preferentially sorbed, exhibiting greater affinity for the sorbents compared to Cd2+ as shown by its relatively higher uptake onto the sorbents than Cd2+. The maximum sorption capacities for NaMMT and PMMAgMMT were 18.73 and 19.27 mg/g for Cd2+, and 30.03 and 34.25 mg/g for Pb2+, respectively. The sorption data obeyed the Langmuir model and the pseudo-second order kinetic model with R 2 of at least 0.9800 for both models. The sorbents could also be regenerated up to three cycles without a significant loss in the sorption capacity. FTIR measurements showed the presence of metal–oxygen bonds after sorption, confirming the occurrence of adsorption as one of the heavy metal removal processes. The work demonstrated the potential of using low-cost nanoscale composite material for the removal of Cd2+ and Pb2+ from aqueous solution.
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    Preparation and Structural Properties of Electrospun PAN Nanofibers Reinforced With ZnS Nanoparticles
    (Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 2015-02-04) Onwudiwe, Damian C.; Strydom, Christien A.; Vala, Remy M. K.; Tichagwa, Lilian
    Polymer nanocomposite fibers based on polyacrylonitrile (PAN), reinforced with different morphologies of ZnS nanoparticles at different percentage loadings were prepared using the electrospinning method. The thermal decomposition profile of the nanofibers was investigated using thermogravimetric analysis (TGA). The morphology and structure of the nanofibers were studied by scanning electron microscopy (SEM) and X-ray diffraction. TGA results indicated an enhanced thermal stability of the fibers after incorporation of the nanoparticles. SEM images indicated a linear relationship between the diameter of the PAN-ZnS fibers and the concentration of the hybrid composite solution. X-ray diffraction showed that the ZnS nanoparticles were in cubic phase.
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    Equilibrium and kinetic studies on the adsorption of humic acid onto cellulose and powdered activated carbon
    (Taylor & Francis, 2015-08-24) Tavengwaa, Nikita Tawanda; Chimuka, Luke; Tichagwa, Lilian
    The removal of humic acid (HA) from aqueous solution onto cellulose (CE) and powdered activated carbon (PAC) was investigated in a batch adsorption system as a function of pH, sorbent mass and contact time. The optimum conditions for HA uptake by CE were 2–3, 50 mg and 30 min, respectively. For PAC, they were 2, 50 mg and 30 min, respectively. PAC and CE sorbents were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The kinetic adsorption data was analysed on the basis of Lagergren pseudo-first-order, pseudo-second-order, Bangham and the interparticle diffusion models. The Lagergren pseudo-first-order fitted the kinetic data best. Experimental sorption data were fitted on different adsorption isotherm models, and it was established that the fitting followed the order: Langmuir > Freundlich > Temkin > Dubinin–Radushkevich (D–R). According to the Langmuir isotherm models, the maximum adsorption capacities of CE and PAC for HA were 89.3 and 30.4 mg g−1 , respectively.
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    Synthesis and Characterisation of Ag and Nitrogen Doped Tio2 Nanoparticles Supported on A Chitosan-Pvae Nanofibre
    (International Journal of Advanced Research in Chemical Science (IJARCS), 2014-04-04) Ocwelwang, Atsile Rosy; Tichagwa, Lilian
    In this studythe sol gel synthesis method was employed for the preparation of nitrogen and silver-doped TiO2nanoparticles.This was followed by immobilising the prepared nanoparticles onto chitosan (Cs) and polyvinyl alcohol-co-ethylene (PVAE) polymer fibres using the process of electrospinning. This was done so as to secure the particles on the Cs/PVAE matrix to allow their use in applications such as water treatment. Characterisation was carried out to establish some physical properties of the prepared particles. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Energy-dispersive x-ray Spectroscopy (EDX) were used to analyze the size, morphology and composition of the nanomaterials. Fourier Transform Infrared (FTIR) spectroscopy was used to monitor reactions and for identification of functional groups while X-ray diffraction (XRD) analysis was carried out to determine the crystalline phases of the synthesized material. The crystallite size was calculated using the Scherrer equation and the thermal stability of the nanocomposites was determined using Thermogravimetric analysis(TGA).The XRD patterns showed that the undoped and doped samples consisted of mixed crystalline phases of anatase and rutile. The diameter of randomly selected nanoparticles was found to range from 6.4 nm to 21 nm while the size of the nanofibres was found to be in the range 234-270 nm. Nitrogen doped titania nanoparticles were the smallest in size.
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    Photo-catalytic activity of carbon/nitrogen doped TiO2-SiO2 under UV and visible light irradiation
    (Materials Science Forum, 2012-12-27) Mungondori, Henry H.; Tichagwa, Lilian
    The sol gel synthesis method was used to prepare carbon and nitrogen doped titanium dioxide (TiO2) photo-catalyst using titanium tetrachloride (TiCl4) as the precursor. Doping was carried out to modify the absorption band edge of titanium dioxide. To avert the problem associated with use of powder TiO2, the photo-catalyst was immobilized on glass support using tetraethyl orthosilicate (TEOS), which served as a binder and precursor for silicon dioxide (SiO2). The prepared photo-catalytic materials were characterized by FT-IR, XRD, TEM, BET and DRS. The photo-catalytic efficiency of titanium dioxide immobilized on glass support was evaluated using the degradation of methyl orange (MeO) and phenol red (PRed) under ultraviolet and visible light irradiation. Doping with carbon and nitrogen, and incorporation of silicon dioxide into the titanium dioxide matrix allowed utilization of visible light by the prepared TiO2-SiO2 nano-composites. Photo-degradation tests were carried out for doped and undoped photo-catalyst. An increased rate of photo-oxidation of methyl orange and phenol red was observed under visible light irradiation as compared to UV light irradiation.
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    Synthesis of Oligomers of 12-Acryloyloxydodecanoic Acid via Reversible Addition Fragmentation Transfer (RAFT) Polymerisation
    (International Journal of Chemistry, 2009-08-05) Tichagwa, Lilian; Sanderson, Ron; Pasch, Harald
    A long chain fatty acid carrying an acryloyl functionality, 12-acryloyloxydodecanoic acid (12-ADA), was prepared from 11-hydroxydodecanoic acid and acryloyl chloride and used as monomer in the synthesis of oligomers of 12-ADA via the RAFT controlled polymerisation process. Reversible Addition Fragmentation Transfer (RAFT) reagents were prepared and used to control the polymerisation process and produced an oligomeric product with few monomeric units instead of a high molecular weight polymer of 12-ADA. The transfer reagents were prepared from Grignar intermediates from a reaction of dithioacids with free radical initiators 2,2-azobisisobutyronitrile (AIBN) and 4,4-azobis(4-cyanopropanoic acid) (ACP). It was found that short-chain oligomers in the form of dimers and trimers characterized by Electrospray Mass Spectrometry, ESMS and Gel Permeation chromatography, GPC were the major products obtained when RAFT reagents had been used in the controlled polymerisation. As a control, polymerisation was carried out in the absence of RAFT reagents and high molecular-weight polymers were obtained. This confirmed the effectiveness of the prepared RAFT reagents as polymerisation controllers and provided a way for the synthesis of oligomers. Here, the preparation of oligomers of 12-ADA using AIBN-RAFT reagents is reported. The method is expected to provide one way of preparing oligomers of controlled chain length/molecular mass which also carry a carboxylic acid functional group at one end.